The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services. High Speed Downlink Packet Access (HSDPA) improves the radio capacity in the downlink and provides a maximum data rate of 10 Mbps. HSDPA achieves higher data speeds is by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following briefly described below: shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
In shared channel transmission, radio resources, like spreading codes and transmission power in the case of Code Division Multiple Access (CDMA)-based transmission, are shared between users using time multiplexing. A high speed-downlink shared channel is one example of shared channel transmission. One significant benefit of shared channel transmission is more efficient utilization of available code resources as compared to dedicated channels. Higher data rates may also be attained using higher order modulation, which is more bandwidth efficient than lower order modulation, when channel conditions are favorable.
Radio channel conditions experienced on different communication links typically vary significantly, both in time and between different positions in the cell. In traditional CDMA systems, power control compensates for differences in variations in instantaneous radio channel conditions. With this type of power control, a larger part of the total available cell power may be allocated to communication links with bad channel conditions to ensure quality of service to all communication links. But radio resources are more efficiently utilized when allocated to communication links with good channel conditions. For services that do not require a specific data rate, such as many best effort services, rate control or adjustment can be used to ensure there is sufficient energy received per information bit for all communication links as an alternative to power control. By adjusting the channel coding rate and/or adjusting the modulation scheme, the data rate can be adjusted to compensate for variations and differences in instantaneous channel conditions.
For maximum cell throughput, radio resources may be scheduled to the communication link having the best instantaneous channel condition. Rapid channel dependent scheduling performed at the bases station allows for very high data rates at each scheduling instance and thus maximizes overall system throughput. Hybrid ARQ with soft combining increases the effective received signal-to-interference ratio for each transmission and thus increases the probability for correct decoding of retransmissions compared to conventional ARQ. Greater efficiency in ARQ increases the effective throughput over a shared channel.
FIG. 1 illustrates a high speed shared channel concept where multiple users 1, 2, and 3 provide data to a high speed channel (HSC) controller that functions as a high speed scheduler by multiplexing user information for transmission over the entire HS-DSCH bandwidth in time-multiplexed intervals. For example, during the first time interval shown in FIG. 1, user 3 transmits over the HS-DSCH and may use all of the bandwidth allotted to the HS-DSCH. During the next time interval, user 1 transmits over the HS-DSCH, the next time interval user 2 transmits, the next time interval user 1 transmits, etc.
High-speed data transmission is achieved by allocating a significant number of spreading codes (i.e., radio resources in CDMA systems) to the HS-DSCH. FIG. 2 illustrates an example code tree with a fixed Spreading Factor (SF) of sixteen. A subset those sixteen codes, e.g., twelve, is allocated to the high-speed shared channel. The remaining spreading codes, e.g., four are shown in the figure, are used for other radio channels like dedicated, common, and broadcast channels.
Although not necessarily preferred, it is also possible to use code multiplexing along with time multiplexing. Code multiplexing may be useful, for example, in low volume transmission situations. FIG. 3 illustrates allocating multiple spreading codes to users 1, 2, and 3 in code and time multiplexed fashion. During transmission time interval (TTI) 1, user 1 employs twelve codes. During transmission time interval 2, user 2 employs twelve spreading codes. However, in transmission time interval 3, user 1 uses two of the codes, and user 3 uses the remaining ten codes. The same code distribution occurs in TTI=4. In TTI=5, user 3 uses two of the codes while user 2 uses the remaining codes.
With HSDPA and other features being added to new 3GPP releases, the dedicated resource cost to maintain an already-established HSC connection is relatively low from both the network and the UE subscriber perspective. A resource cost is any hardware or software resource allocated to support a radio connection. Example resource costs include: uplink and downlink transmit power, uplink and downlink spreading and channelization codes, radio base station hardware resources, data processing costs like memory storage and computational operations processed, and communication resources between nodes in the radio network used to monitor and maintain a connection, etc. This is because low activity users for which an HSC connection has already been established are not scheduled for transmission when there is no data to send. But there is some amount of resources required to maintain each HSC connection, and there is a limit to the number of HSC connections that can be maintained. While perhaps convenient for users to have their already-established HSC connections remain at the ready for possible future data transmission, it is still a waste of resources that could be used for other users that actually currently need those occupied resources. This is also the case for users for which a dedicated traffic channel is initially established, but are not currently actively using the capacity of that dedicated channel, on the uplink and/or on the downlink.
System throughput, accessibility, and retainability will suffer unnecessarily. For example, the downlink code tree in a CDMA-based communications system has a fixed size for each cell. The number of possible users in the code tree depends on the spreading factor (SF) of the connections, (e.g., SF=256=>256 users, SF=128=>128 users, SF=64=>64 etc). If a first user is allocated to a HSC, the first user “consumes” one code position of the code tree, thereby preventing a second user from using that one code position in the code tree. If the first user is not actively transmitting or receiving, and the second user with data to be sent or received is denied transmission because there is no free downlink code transmit, then the second user is not serviced (denied access). The HSC is also used less efficiently transferring less data than it could, i.e., the HSC throughput is lower.
Due to user mobility and radio variations, the total transmit power required by all established connections may occasionally become too high. In those situations, the system may be required to disconnect one or more connections to decrease that total power. It would be better if the mobile communications network first reduced the power by disconnecting those connections transmitting little or no data. By making these unused or lightly used resources available for active users, it is also less likely that active users are rejected (due to lack of resources in the cell) or dropped when performing a cell handover to another cell.
Consequently, the data transmission activity of established connections is monitored along with a measure of the load or drain on communication resources. When the load on communication resources increases or when it moves past a threshold, inactivity over an connection is not permitted or is permitted for a shorter time before releasing that user's connection. On the other hand, a lower load allows for a longer (or no) inactivity period before disconnecting the connection. Once inactivity on a connection exceeds the time determined based on load, that connection may be transferred to a lower capacity channel, e.g., a common channel. Alternatively, that inactive connection may be disconnected.
Although applicable to any type of channel for which a mobile user connection can be established and maintained, (and thereby consuming resources), in one non-limiting, example implementation, a mobile communications network supports mobile radio communication over multiple cell coverage areas, with at least one of the cell coverage areas including a high speed shared radio channel (HSC). A load associated with the high speed shared radio channel is determined. An activity level is detected for the high speed shared radio channel connection. If the HSC connection is detected as being inactive, a corresponding inactivity time period is determined for the high speed shared radio channel connection based on the detected load. During the inactivity time period, the activity level of the high speed shared radio channel connection is monitored to determine whether resources allocated for the high speed shared radio channel connection should be released. Similar procedures may be applied to each of multiple high speed shared radio channel connections on the high speed shared radio channel as well as to multiple high speed shared radio channels.
The load may be determined based on one or more of the following example load parameters: data processing resources, hardware utilization, allocated radio channel resources, power, number of users on the high speed shared radio channel, or interference. An inactive high speed shared radio channel connection may be detected when a corresponding amount of data to transmit over the high speed shared radio channel is less than a predetermined amount. Optionally, that inactivity threshold detection may have to be sustained for a predetermined period of time before concluding that the connection is inactive to avoid making a premature inactivity decision.
The activity timer for a high speed shared radio channel connection detected as inactive may be inactivated if the connection's activity level exceeds an activity threshold (optionally the level exceeds the threshold for a predetermined time period). If the monitored activity level does not exceed the activity threshold by the time the inactivity time period is over, the allocated resources for the HSC connection are released, and the user connected transferred to a lower capacity channel such as a common channel. Also, if the monitored activity level does not increase above an activity threshold by the time the inactivity time period is over, a state of the detected high speed shared radio channel may be changed from an active state to another state.